Abrasion Resistance?

My first suggestion is that you check on stellite http://en.wikipedia.org/wiki/Stellite It has outstanding wear, thermal and abrasion resistance - which are three reasons it is used for valve seats. If you don't require a metal, you might consider using ceramic for this application.

Do you consider the manufacturing of diesel injectors ?

If yes than due to small dimensions you should think about alloys and not stellite which is used as deposit on a steel carrier.

The value of E (young modulus) decreases for steel with about 250...350 ppm/K.

For a pair injector-needle the effect will be an increase of radial gap and back leak.

Usually high alloyed steels are used with a hardness in the range of 60HRc.

I do not wish to mass produce the injectors the final material used will probably vary somewhat. I need a material to start out with for design testing. Testing will take I suspect no less than 5hrs.and possibly into the hundreds if the original design needs no Major redesign.

For such experiments use a steel same as for roller bearings according to european satandrds 100 C6 for instance. In fact pieces of this steel will work properly for much more than you expect.

I guess we should contact the engine manufacturers and advise they remove all the stellite components (such as valve seats) from their engines because nick name says stellite is only for hard surfacing. Frankly, I don't know what the best material choice is, but from the way OP's inquiry was worded, I think stellite shouldn't be ruled out. I have several applications where my stellite knife blades outlast my high alloy 60HRc steel blades.

Thank you for ironic comment.

The reason I mentioned stellite as a material to be deposit is that due to cost and difficulty to manufacture (in the wikipedia those problems are mentioned exactly where the other indications are given) it is very often used as a wear resistant layer deposit, made by welding usually, this being the reason welderman knows about it.

Working conditions of a seat valve and a valve are quite different from those of an injector needle.

The needle of a injector is a small part, cooled also by the oil jet and by the contact with the seat when it is not open. So that if the jet has no abrasive particles any steel hard enough can be used. The situation is quite different for a valve seat in contact with high speed hot gas and, when the valve is closed, with a part heated by the hot gases the seat being the element which leads major part of the heat from the valve poppet to the cylinder head.

I recommended the steel quality because many years ago I was obliged to make spare parts for a special engine for which replacement was not any more available and high carburised steels were used. The advantages were a high hardness wear resistant layer combined with an easy manufacturing before heat treatment and a good acceptance of grinding + lapping for the finish (low roughness and low form and dimensional tolerances since the gap is in the range of 1µm, a needle should fall slowly without stops under own weight in its housing). This solution was adopted for the "long range" usage and gave fully satisfactory results. After a time we tested as well steel with a higher content in carbon (for the hardness) and came across the mentioned steel which has as well a high content of Cr. The hardness can reach HRc 62..64 and it is for the usual needle/body dimensions more economical than previous solution.

From an other point of view if we look at the wikipedia information stellite is mostly cast in order to avoid too expensive massive machining. It would be a too expensive approach for what is expected.

In general a suggestion should be matched to the requirement and be as near as possible to the optimum.

I prefer to avoid the politics of engineering which is precisely what you are engaging in when you deduce my sources of information and when you denigrate alternate materials to promote your choice. If steel performs best, show us the data. We routinely machine stellite into micron tolerance components. Low sulfur fuels result in lower lubricity and place a premium on abrasion resistance. The water content of the fuel also has a deleterious affect. High alloy steel injectors have been known to seize in a few hours of operation. Ceramic (zirconia alloys), glass, and other materials have been under investigation for at least 15 years as a result of this problem.

OK I may be wrong and you are right, for me it is not as a problem as it is for you.

Please tell me which are the materials used TODAY for the manufacturing of injectors.

I do not consider as politics what I wrote. Your name is WELDERMAN so that I assumed -may be was I wrong - that your choice was following your speciality. Since most of applications I met and where stellite was used were based on a deposit by electro-welding on a steel support (process valves at high temperature and fluid velocity) I assumed that you met the product in the frame of this technology. If you consider this as an insult I apologize it was not my intention.

I am sincerely sorry that I cannot show you data since :

1- the replacement was done over 30 years ago

2- we were not a lab to make research and keep track of the results, we were a production plant and our approach was very pragmatic, we made the parts put them on the engine and tested at different power levels and speeds (on a brake) for a limited number of hours. The engine run smoothly we did not notice any changes so that we assumed that we could make a field test. And even if you do not believe with the risk to disturb you the engine worked till its following maintenance without any problem under field conditions. If you expect any other data I have not. You are free to accept or not what I wrote.

3- As mentioned my knowledge about stellite was and is limited, it seems that you know a lot more so that please help me learn some more:

- how did you machine cylindrical parts with a diameter of 3 to 6 (≤10)mm ?

- how did you machine the bore for the needle? drilling ? electro-erosion? grinding?lapping? was it a through hole or not (most needles have a conical seat)?

Please give me an example so that I can benefit from what you know. I did my best trying to make the OP benefit from MY knowledge and practical experience. Please do the same for me.

4- I totally disagree with the term you used "denigrate". To have an opinion different from yours and bring arguments to support it does not mean that I denigrate a material or an idea.

It ONLY means that according to MY knowledge (and fortunately all of us have limited knowledge so that we can have the pleasure to learn continuously) I had an other opinion.

There is no absolute solution in engineering a solution depends of many constrains as specification, economics, available technology and skills of personnel aso.. I am very surprised that, as an engineer, you can make usage of this notion!

Do you think that your suggestions are always the best and that no other alternative is possible?

I do not. In the frame of a thread I mention what I consider my basic rule, some body took it as statement I saw later : "the more you know the more you know that you know nothing".

I already stated that I don't know what the best metal is for injector components but advised considering stellite as an option as well as some non metals. You are the one who advised OP not to consider stellite, and now you ask me how to machine it. Please consider starting a thread of your own instead of hijacking this one. I don't know why OP asked for advise on metallic injector components. From what I have read, all the new high tech stuff is non-metallic. Check out Cummings Diesel. They make decent engines and talk openly about their ceramic injectors.

oddog

I can't go into detail why I chose glass for just this application but here is a PDF

http://www.schott.com/poland/polish/download/schott_techn_glaeser_e.pdf

that might be of interest to you. If you find any solution, hint, be it only at first glance, then there are many others to look into.

Sapphires are used in water jet applications and are the material of choice. Their physical properties exceed the demands you are looking at. For machining have a look at

http://spie.org/x8679.xml?ArticleID=x8679

Hope this helps, it did assist me, Ky.